A laminated wiring member in which an insulation layer containing a resin is interposed between two electrodes is used in various devices such as a semiconductor device (e.g., a semiconductor transistor), a capacitance touch panel sensor, and a printed board (e.g., a flexible printed board (FPC)). Such a laminated wiring member typically has a structure in which a contact hole is formed in the insulation layer and both the electrodes are connected in the contact hole.
As a formation method of the insulation layer provided with the contact hole, a method of removing a part of an insulation film formed entirely over a board by means of photolithography and etching is typically used. Particularly, in an organic thin-film transistor provided by using an organic semiconductor for a semiconductor layer of a semiconductor transistor, since the semiconductor layer often exhibits a poor tolerance against an organic solvent, an insulation film is required as a passivation layer on an upper side of the semiconductor layer. Moreover, particularly when a low-molecular organic semiconductor such as pentacene is used, the semiconductor layer exhibits a poor tolerance against the organic solvent. As the passivation layer in such a case, use of a fluorinated insulation film typified by CYTOP has been studied. However, since an ink used for fluorinated insulation film has a small surface tension, it is difficult to perform a patterning by ink jet printing (IJ), plate printing or the like. Accordingly, after forming the fluorinated insulation film entirely over the board by spin coating or the like, it is required to employ a method of removing a part of the fluorinated insulation film by photolithography, etching or the like.
In order to solve the above problem, for instance, Patent Literature 1 discloses a through-hole formation method including: disposing a core material on a conductive layer; laminating a film over the core material; and removing a part of the film corresponding to or around the core material to make a hole. Patent Literature 2 discloses a contact hole formation method including: forming a removable pillar on a base material; forming an insulation layer on a side of the base material where the pillar is formed; and removing the pillar to make a contact hole in the insulation layer.
However, these methods require a removing step of the core material or the pillar and it may happen that a residue of the core material and the pillar disadvantageously remains in the contact hole. Moreover, since an electrostatic suction-type liquid drop discharge method is used for forming the pillar in the method of Patent Literature 2, it takes time for the step, so that productivity is adversely affected.
Patent Literature 3 discloses a method of forming a VIA post, and subsequently forming an interlayer insulation film by using a screen plate having a non-discharge region slightly larger than a head of the VIA post. However, it is difficult to form a minute VIA post since screen printing is used. Moreover, a material of the interlayer insulation film is limited to a material to which screen printing is applicable.
Patent Literature 4 discloses a method of forming a VIA directly on a wiring pattern provided on a board by inkjet printing in such a shape that ends of the VIA project beyond a middle portion thereof. However, since a projecting periphery of a conductive portion is used in this method, an available conductive area is diminished as the formed conductive portion becomes small. Moreover, it is difficult to completely reproduce the shape of the VIA with respect to all the VIAs.